Hydrocracking of hydrocarbon feedstocks is often used to convert lower value hydrocarbon fractions into higher value products, such as conversion of vacuum gas oil (VGO) feedstocks to various fuels and lubricants. Typical hydrocracking reaction schemes can include an initial hydrotreatment step, a hydrocracking step, and a post hydrotreatment step, such as dewaxing or hydrofinishing. After these steps, the effluent can be fractionated to separate out a desired diesel fuel and/or lubricant oil base oil.
A process train for hydrocracking a feedstock can be designed to emphasize the production of fuels or the production of lubricant base oils. During fuels hydrocracking, typically the goal of the hydrocracking is to cause conversion of higher boiling point molecules to molecules boiling in a desired range, such as the diesel boiling range, kerosene boiling range, and/or naphtha boiling range. Many types of fuels hydrocracking processes also generate a bottoms component from hydrocracking that potentially can be used as a lubricant base oil. However, the lubricant base oil is produced in a lesser amount, and often is recycled and/or hydrocracked again to increase the fuels yield. In hydrocracking for forming a lubricant base oil the goal of the hydrocracking is typically to remove contaminants and/or provide viscosity index uplift for the feed. This results in some feed conversion, however, so that a hydrocracking process for generating a lubricant base oil typically produces a lesser amount of fractions that boil in the diesel boiling range, kerosene boiling range, and/or naphtha boiling range. Due to the difference in the desired goats, the overall process conditions during fuels hydrocracking of a given feedstock typically differ from the overall process conditions during hydrocracking for lubricant base oil production on a similar type of feedstock.
U.S. Pat. No. 6,884,339 describes a method for processing a feed to produce a lubricant base oils. A feed is hydrotreated and then hydrocracked without intermediate separation. An example of the catalyst for hydrocracking can be a supported Y or beta zeolite. The catalyst also includes a hydro-dehydrogenating metal, such as a combination of Ni and Mo. The hydrotreated, hydrocracked effluent is then atmospherically distilled. The portion boiling above 340° C. is catalytically dewaxed in the presence of a bound molecular sieve that includes a hydro-dehydrogenating element. The molecular sieve can be ZSM-48, EU-2, EU-11, or ZBM-30. The hydro-dehydrogenating element can be a noble Group VIII metal, such as Pt or Pd. A distillate fraction is mentioned as a possible additional product, the distillate fraction having a pour point of less than about −20° C., a total aromatics content of less than 2 wt %, a polyaromatic compounds content of less than 1 wt %, and a cetane index of about 52 or more. The amount of this distillate fraction is not specified.
U.S. Pat. No. 7,371,315 describes a method for producing a lubricant base oils. A feed is provided with a sulfur content of less than 1000 wppm. Optionally, the feed can be a hydrotreated feed. Optionally, the feed can be a hydrocracked feed, such as a feed hydrocracked in the presence of a zeolite Y-containing catalyst. The feed is converted on a noble metal on an acidic support. This entire converted feed can be dewaxed in the presence of a dewaxing catalyst. A distillate fraction with a pour point of −20° C. and a cetane value of 50 is mentioned as a possible additional product, but the amount of this distillate fraction is not specified.
U.S. Pat. No. 7,250,106 describes a method for producing lubricant base oils by hydroprocessing a feedstock over a specialized catalyst followed by dewaxing of at least a portion of the effluent. A gas oil (distillate) with a pour point of −18° C. and cetane number of 60 is reported as a side product.